The invention relates to stable anthelmintic compositions combining two or more active compounds.
When formulating anthelmintic compositions it is necessary that the compositions maintain the stability of the active compounds in those compositions. In particular, it is necessary to maintain the stability in order to allow for the compositions to be prepared well in advance of their intended use.
UK Patent Specifications 2166436, 2176182 and 2187742 and EP170006 describe antibiotic compounds, designated Antibiotics S541, prepared by fermentation of Streptomyces microorganisms and chemical derivatives thereof. The disclosure of these UK and EP documents are incorporated herein by reference. Such compounds have antibiotic, and, in particular, anti-endoparasatic, anti-ectoparasitic, anti-fungal, insecticidal, nematicidal and acaricidal activity and are of special use in agriculture, horticulture and animal and human health. These compounds include the avermectin and milbemycin groups of compounds.
EP329460 discloses that the stability of these antibiotic compounds can be enhanced when they are in the presence of an antioxidant. In particular, EP329460 refers the stabilisation of a group of Antibiotic S541 derivatives described in UK2192630A and in particular to 23[E]-methoxyimino Factor A, also known as moxidectin. A variety of antioxidants are disclosed in EP329460 as useful for stabilisation (which are herein incorporated by way of reference) with particular reference to butylated hydroxytoluene (BHT). These antioxidants are disclosed as being present in amounts ranging from 0.005 to 1% with respect to the antibiotic compounds.
It has now been discovered that these antibiotic compounds may be unstable when in the presence of an antioxidant as described in EP329460, when the antiobiotic compounds are combined with another active material to form a combination anthelmintic composition.
It is an object of the invention to provide a stable anthelmintic composition including antibiotic compounds as described above together with other active compounds.
Other objects of the invention will be apparent to those skilled in the art from the description and examples provided herein.
In broad terms, according to one aspect of the invention, there is provided an anthelmintic composition including an avermectin or a milbemycin, together with praziquantel, wherein the composition is stabilised by between about 0.15% and about 5.0% of an antioxidant by weight of the composition.
In broad terms, according to another aspect of the invention, there is provided an anthelmintic composition combining an Antibiotic S541 compound preparable by fermentation of a Streptomyces microorganism, or a chemical derivative thereof, and another anthelmintically active compound, wherein the composition is stabilised by between about 0.15% and about 5.0% of an antioxidant by weight of the total anthelmintic composition.
In broad terms, according to a further aspect of the invention, there is provided a method of stabilising an anthelmintic composition which combines an Antibiotic S541 compound preparable by fermentation of a Streptomyces micro organism, or a chemical derivative thereof, and another anthelmintically active compound, the method including the addition of between about 0.15% and about 5.0% of an antioxidant by weight of the total composition.
Preferably the amount of the antioxidant is between about 0.2% and about 3.0% by weight of the total composition and more preferably is between about 0.2% and 0.3% by weight of the total composition. Most preferably the amount is 0.25% by weight.
Preferably the amount of antioxidant is in addition to antioxidant used to stabilise the Antibiotic S541 compound or derivative prior to its inclusion in the anthelmintic composition.
Preferably the antioxidant is one which is capable of reacting with free radicals and may be a C1-12 alkyl gallate, benzyl hydroxybenzoate, butylated hydroxyanisole, butylated hydroxytoluene, quinones and salts thereof, nodihydroguaiaretic acid, or tocopherols.
Preferably the antioxidant is butylated hydroxytoluene (BHT).
Preferably the Antibiotic S541 compound or derivative thereof is an avermectin or a milbemycin.
Preferably the Antibiotic S541 compound or derivative is abamectin, ivermectin, doramectin, selemectin or moxidectin.
Preferably the anthelmintically active compound is an insoluble compound such as praziquantel or an insoluble benzimidazole.
Preferably the composition is an oral drench composition.
In another aspect, the invention may be seen to be an oral anthelmintic drench formulation including moxidectin technical concentrate (MTC) or moxidectin technical material (MTM), and praziquantel, wherein the formulation is stabilised by the inclusion of between about 0.15% and about 5.0% of BHT by weight of the formulation, the BHT being in addition to BHT present in the MTC or MTM.
This invention relates generally to improvements in the stability of anthelmintic compositions which include, as one of the active components, the Antibiotics S541 which have been referred to previously herein. As has been stated, the use of antioxidants, such as BHT, to stabilise certain antibiotic compounds is known. This knowledge is used in the preparation of technical material and technical concentrate solutions of antibiotic compounds, such as those derived from the fermentation of Streptomyces microorganisms, and chemical derivatives thereof, which are later used for the preparation of veterinary and human pharmaceutical compositions.
Typical antibiotic compounds of use in the compositions according to the invention are the avermectins (e.g., abamectin, ivermectin, doramectin, selemectin) and the milbemycins (e.g., moxidectin).
A particular example is the production of moxidectin technical material and moxidextin technical concentrate, both of which include between about 0.3 and 0.6% of the antioxidant BHT. This technical material or concentrate can be stored for a suitable length of time in order that commercial products can be prepared which include the active material. For example, the American Cyanamid Company products CYDECTIN(copyright) and VETDECTIN(copyright) liquid compositions are prepared using moxidectin technical material or moxidectin technical concentrate. Both these commercial products have excellent stability as is well known.
Both CYDECTIN(copyright) and VETDECTIN(copyright) include one active material, moxidectin, which is stabilised by the BHT originally present in the technical material or concentrate of moxidectin used to produce the commercial product.
It is therefore surprising that when this moxidectin technical material or concentrate is used to produce an anthelmintic composition that combines moxidectin with another anthelmintic compound, suitable stability of the moxidectin was not achieved. This difficulty has been specifically observed when the other anthelmintic compound used in the composition is the insoluble compound praziquantel present in the composition as a suspension. Without wishing to be bound by this, as the other individual components in the formulation are relatively standard in the formulation art, it seems that it may be an effect of the insoluble praziquantel that destabilises the moxidectin. It is also possible that it is an effect of the combination of components required to keep the praziquantel in suspension in the formulation that results in this destabilising effect.
In order to achieve stability of moxidectin to suitable levels (e.g., above 95% for longer than three (3) months) it has been found necessary to include additional amounts of an antioxidant such as BHT into the formulation. A suitable amount of additional antioxidant is above about 0.15% of antioxidant by weight of the total composition and preferably below about 5.0% by weight. More preferably, the amount of BHT added by weight of the total composition is between 0.2% and 3.0% and more preferably between about 0.2% and 0.5% by weight of the composition. Most preferably the amount is about 0.25% by weight.
It is hypothesised that, as other antibiotic compounds in the S541 series can also be stabilised by antioxidants such as BHT, their use with insoluble compounds such as praziquantel will also require additional antioxidant to maintain stability. Further, it is hypothesised that the inclusion of other insoluble anthelmintics, such as the insoluble benzimidazoles, may also affect the stability of the antibiotic compounds when used in combination.
The antioxidant of preferred use in the compositions according to the invention is butylated hydroxytoluene (BHT). Other antioxidants could also include those disclosed in EP329460 such as those which are capable of reacting with free radicals, including a C1-12 alkyl gallate, benzyl hydroxybenzoate, butylated hydroxyanisole, quinones and salts thereof, nodihydroguaiaretic acid, or tocopherols.
It is known that compounds such as citric or phosphoric acid can act as synergists for some antioxidants such as butylated hydroxyanisole (BHA). It may be that it is necessary for the compositions to include both the extra antioxidant and citric acid to allow the stability levels needed, to be achieved. Preferably the composition will also include between about 0.1% and 1.5% w/v of citric or phosphoric acid. Such compounds are usually present primarily as a buffering agent.
The invention can therefore also be seen to be directed to a method of preparing a stable composition which combines an Antibiotic S541 compound, or chemical derivative thereof (preferably an avermectin or milbemycin), with another anthelmintically active compound, which is preferably praziquantel, wherein the method includes the step of adding between about 0.15% and about 5.0% by weight of the total composition of an antioxidant, which is preferably BHT. In a preferred form the method will include the addition of moxidictin via moxidectin technical material (MTM) or concentrate (MTC) and the amount of BHT added will be in addition to the BHT originally present in the MTM or MTC. In a further preferred form the method will also include the addition of citric acid.
Where compositions according to the invention are to be used or be prepared for use, in human or veterinary medicine, or in agriculture, horticulture or forestry, they may also contain one or more suitable carriers or excipients as will be known in the art. The compositions are preferably oral drench compositions but could also be formulated as injectables or feed additives as will be known in the art.